/Engine/Source/Runtime/Engine/Public/GeomTools.h
Util to see if P lies within triangle created by A, B and C.
namespace FGeomTools { bool FGeomTools::PointInTriangle ( const FVector3f & A, const FVector3f & B, const FVector3f & C, const FVector3f & P, const float InsideTriangleDotProductEpsilon ) }